1. Field of the Invention
The present invention relates to exposure methods, exposure apparatuses, and device manufacturing methods, and more particularly to an exposure method and an exposure apparatus used in a lithography process to manufacture microdevices (electronic devices) such as a semiconductor device, and a device manufacturing method using the exposure method or the exposure apparatus.
2. Description of the Background Art
Conventionally, in a lithography process for manufacturing electron devices (microdevices) such as semiconductor devices (such as integrated circuits) and liquid crystal display devices, exposure apparatuses such as a projection exposure apparatus by a step-and-repeat method (a so-called stepper), or a projection exposure apparatus by a step-and-scan method (a so-called scanning stepper (which is also called a scanner) is mainly used.
In these types of exposure apparatuses, with finer device patterns due to higher integration of semiconductor devices, requirements for high overlay accuracy (alignment accuracy) is increasing. Therefore, requirements for higher accuracy is increasing, also in position measurement of substrates such as a wafer and the like on which a pattern is formed.
As an apparatus to meet such requirements, for example, in U.S. Patent Application Publication No. 2006/0227309, an exposure apparatus is proposed which is equipped with a position measurement system using a plurality of encoder type sensors (encoder heads) installed on a substrate table. In this exposure apparatus, the encoder head irradiates a measurement beam on a scale which is placed facing a substrate table, and measures the position of the substrate table by receiving a return beam from the scale. In the position measurement system disclosed in U.S. Patent Application Publication No. 2006/0227309 and the like, it is desirable for the scale to cover as much movement area of the substrate table as possible, except for the area right under the projection optical system. Therefore, a scale with a large area becomes necessary; however, to make a highly precise scale having a large area is very difficult, as well as costly. Accordingly, a plurality of small-area scales are usually made which is the scale divided into a plurality of sections, and then the small-scales are combined. Accordingly, while it is desirable for the alignment performed on the plurality of scales to be accurate, it is difficult in reality to make a scale with no individual difference, and to put the scales together without any errors.